The invention relates generally to an overhead conveyor, and more particularly it relates to a conveyor of the type which has a track installation with at least one track switch point, a trolley carriage suspended on the installation, switch point operating means including guiding rails and interlocking rails secured to the track installation, a switch roller arranged on a lever which is pivotably supported on the trolley carriage, the rollers cooperating with the guiding and interlocking rails, and being controlled by an adjustment device arranged on the carriage and being responsive to control signals to angularly offset the lever according to the desired direction of the carriage, and a safety device including tiltable tongues arranged on the track installation in front of the interlocking rails and controlled by the adjustment device for the lever to provide a sloping surface in the direction of travel of the carriage.
An overhead conveyor of the above-described type is described for example in a special issue of the magazine "Verkehr und Technik", 1977, copies 1-3. The described switch points and overhead track installations for the trolley carriage consist of box-like beams defining at its lower flange a longitudinal slit through which suspension means between the trolley and the carriage such as for example passenger cars, are directed. The track switch due to the diverging longitudinal slot in the branch track defines a switch point gap and consequently in order to stabilize the position of the carriage when passing through this gap it is necessary to provide switch guiding rails on the track installation and switch guiding rollers in the carriage cooperating with the guiding rails. These guiding rollers are tiltably supported to engage the desired guiding rails so that when the carriage approaches the switch point the desired direction can be selected. Usually, the guiding rollers are arranged in pairs on free ends of cooperating rocking levers pivotably supported on the carriage and controlled into a desired angular position by an adjustment device of the carriage. In order to monitor and also to adjust precisely the angular position of the rocking levers in accordance with the desired direction of advance of the carriage there is also provided a mechanically operated safety device. This known safety device consists of tiltable tongues arranged in the range of the track installation before the switch point, the tongues being operable to be alternately swung up to provide wedge like sloping surfaces cooperating with the raised guiding rollers. The sloping tongues can be also rigidly arranged on the tracks to safeguard the advance of the carriage and prevent its deflection in the undesired direction. The two switching possibilities before a track switch point necessitate the provision of pairs of these safety tongues whereby the tongues in each pair are alternatively activated into the sloping position. In the event that the guiding rollers assume accidentally a wrong position for example due to an erroneous electrical control signal transmitted to the adjustment device, the independently adjusted sloping tongues insure that as soon as slide shoes provided on the rocking levers engage the sloping surfaces the guiding rollers are mechanically swung up into the correct switching position independently of the position of the adjustment device on the carriage. The correct position of the switch guiding rollers no matter whether adjusted by the adjustment device on the carriage or by the safety tongues on the track is further insured against unintentional retraction into an incorrect switching position before the switch point by interlocking rails which in the prior art construction form with the guiding rails a channel surrounding the guiding rollers.
In this practicable prior art conveyor system improvement with respect to the safety of the switching action of the carriage are still desirable. For example, due to the elastic suspension of the trolley carriage the level of the aforedescribed switch point guiding parts arranged in the trolley carriage is dependent on the momentary load condition of the cabin; as a result, the slide shoe on the rocking levers engage the assigned safety tongues at different contact points and consequently the rocking levers with the supported guiding rollers are swung up at different angles. For example if the trolley carriage is unloaded and the construction tolerances accumulate accidentally in an undesired direction, this switching angle of the rocking lever can be so small that the switch point guiding rollers or other parts of the rocking lever collide with the ends of the interlocking rail. Furthermore, in view of the fact that the guiding rollers at one side of the carriage before the switch point have to be swung down into the effective range of the interlocking rails and at the same time the guiding rollers on the other side of the carriage have to be swung up out of the range of the interlocking rails, there must be provided a free space extending in the direction of the travel of the carriage between the end of the safety tongues and the beginning of the interlocking rails. Because of this free spacing however the possibility remains that the correctly inclined nonetheless unlocked rollers can be still tilted for example by means of a false control impulse to reverse its angular position before the rollers reach the locking rails.